POJ1426Find The Multiple dfs

输出结果有点不能理解

#include <algorithm> #include <iostream> #include <stdio.h> #include <queue> #include <string.h> using namespace std; int n; int flag; void dfs(unsigned long long a, int k)//unsigned long long的最大值：18446744073709551615 { if(flag||k==19) return ; if(a%n==0){ printf("%I64u\n", a); flag = 1; return; }else { dfs(a*10,k+1); dfs(a*10+1,k+1); } } int main() { while(~scanf("%d", &n)){ if(n == 0) break; flag = 0; dfs(1,0); } return 0; }